1. Field of the Invention
The present invention is directed to an electrical junction and joint box for use with a solar cell module having solar cells. More specifically, the present invention is directed to an electrical junction and joint box with a housing and electrical and/or electronic means and a connection device provided in the housing.
2. Description of Related Art
Since an output voltage associated with individual solar cells is generally too low to operate electrical devices, such as household appliances or the like, several solar cells are normally interconnected into solar cell modules. On one hand, there is the possibility of series connection of individual solar cells and, on the other, there is the possibility of parallel connection of the solar cells in the solar cell module. The individual currents of the solar cells in parallel connection are added to one another to create an overall current. The solar cells should have essentially the same physical properties so that current required is not increased. In practice, however, parallel connection of solar cells is not normally used, since an individual solar cell can already deliver a current of a few amperes.
When solar cell modules are assembled having multiple solar cells, the solar cells are often series connected. However, a problem can arise when a series connected solar cell module is partially shadowed or obstructed from sunlight, so that a solar cell or individual solar cells of the solar cell module receive less solar radiation, or none at all. The reason for reduced solar irradiation can be, for example, fouling of the solar cells or shadows cast by trees, building facilities or buildings.
In contrast to shadowing of the solar module uniformly over its entire surface, which leads only to a reduction in power, a specific problem arises when a solar cell is subjected to partial shadowing. In normal operation, a common current flows through the series-connected solar cells of the solar cell module, and each individual solar cell, with its respective voltage, contributes to the overall voltage of the solar cell module. However, if one solar cell is shadowed, it no longer generates any voltage and in practice acts as a diode, in the reverse direction, and opposes the current flow in the solar cell module. As a result, the entire module can no longer deliver current, so that the entire operation of the solar cell module is adversely affected.
Moreover, on the shadowed solar cell, a voltage is dependent on the position of the shadowed solar cell in the series circuit. If the voltage is greater than its blocking voltage, a breakdown occurs in the solar cell, and thus, the solar cell is permanently damaged. Even if the solar cell should not be damaged by the breakdown, in the partially shadowed solar cell, a large power loss is converted so that the shadowed solar cell heats up. This heat-up can lead to damage on the shadowed solar cell, as well as surrounding solar cells.
In order to avoid problems associated with partially shadowed solar cells, diodes (e.g., bypass diodes) are often used and are connected antiparallel to the solar cells. This results in that a shadowed solar cell no longer delivers any portion to the total voltage of the solar cell module, but the current flow is nevertheless maintained. The solar cell module thus shows only a reduced operating voltage, but does not break down completely. Moreover, in the shadowed solar cell, power is no longer converted so that damage to the shadowed solar cell can be avoided.
A diode could be assigned to each solar cell of a solar cell module. However, often a plurality of solar cells connected in succession is protected by a common diode. Generally electrical junction and joint boxes, which are used for solar cell modules, thus houses a plurality of bypass diodes. Moreover, in electrical junction and joint boxes there can be other electrical and/or electronic means so that the conductors fed to the electrical junction and joint box are properly connected to electrical and/or electronic means, such as bypass diodes.
The solar cells in a solar cell module are generally connected to one another with thin conductor strips (so-called strings). These conductor strips typically have a thickness of a few tenths of a millimeter (roughly 0.3 mm) and a width of a few millimeters (roughly 3-8 mm). These conductor strips, which connect the individual solar cells of the solar cell module to one another, are routed out of the solar cell module so that the thin conductor strips can be used directly for connection purposes.
To do this, the conductor strips are typically routed into a junction and joint box from underneath. The box includes a removable cover so that contact can be made with the individual conductor strips by hand in an electrical connection device, which is provided in the housing of the junction and joint box. The thin conductor strips which come from the solar cell module, from underneath relative to the housing of the junction and joint box, are generally bent (manually) by 180° in order to then be connected coming from the top in the connection device. This bending is easily possible since the thin conductor strips, which typically consist of metal have low thickness, are very flexible. However, this approach is very complex and time-consuming, and connection faults cannot be easily avoided.